The present invention is directed to a valve arrangement for controlling the flow of an airstream in an air flow system, preferably a suction stream in a dental suction system, wherein the valve arrangement contains a closure element or valve member that creates a valve space on one side and a control space on the other side so that pressure changes in the control space will change the position of the valve member to regulate the size of the valve space and, thus, regulate the flow therethrough.
The above valve arrangements are utilized in apparatus of dental medicine for controlling the suction airstream in a suction system for suctioning water, blood, saliva, tooth material, etc., from the oral cavity of a patient. U.S. Pat. No. 3,763,862, whose disclosure is incorporated herein by reference thereto and which claims priority from German Patent Application P 20 05 567.8, discloses a valve that defines the flow of an airstream and is arranged in the suction or vacuum line of an under-pressure or vacuum generator. As a closure element, the valve contains a membrane that divides the valve housing into an upper control space that is covered by a cover and into a lower space, which is the actual valve space that contains an inlet and outlet channel for the medium. The control space is in communication with the outlet channel via a connecting line. An aeration valve is connected into the connecting line, and this aeration valve connects the control space to the atmosphere when activated. The flow cross section in the valve space can be entirely opened or closed or can only be partially opened with the assistance of this aeration valve acting as a control valve.
Alternate to the above-mentioned aeration valve, the valve arrangement is also disclosed in this prior art wherein a line branches off from the connecting line between the valve space and the control space, with a free end of the line being constantly connected per se to the atmosphere and being capable of being closed by the operator for control as needed. In order to achieve a metering of the suction stream, it is proposed that a choke that is correspondingly actuated by the operator be integrated into this control line. The pressure difference at both sides of the membrane can be influenced with this choke and, thus, the flow of the medium can be controlled.
Another, similarly constructed valve arrangement is disclosed in German Application 38 27 176, which was the basis for European Application 0 355 467. In this reference, the upper control space of the valve is intermittently connected to the atmosphere either by an electromagnetically actuatable pre-control valve or an aeration valve that directly influences the membrane, which is switched on and off with a variable clock frequency. Such an intermittent drive necessarily leads to a high mechanical stress of the control elements.